Semiconductor device manufacturing methods commonly result in a toxic waste gas stream from an evacuated process chamber in which the processing takes place. The waste gas stream is evacuated from the chamber by means of one or more vacuum pumps but the gas stream must generally thereafter be treated to reduce or eliminate the toxicity associated with the component species in the stream.
Semiconductor processing involving ion-implantation is commonly employed and utilises hazardous species including phosphine (PH3), arsine (AsH3) and boron trifluoride (BF3). Such an implantation method may use a secondary vacuum pump, for example a cryopump or a turbomolecular pump, to create a working pressure in the chamber of about 1×10−4 to 1×10−5 mbar, with a primary pump usually employed to back the secondary pump down to less than 1 mbar.
It is also well known to employ purifiers comprising a chemically active “getter” material which forms stable compounds with the species being pumped, thereby removing contaminate or dangerous species. Such purifiers have hitherto been commonly used in sorption pumps.
The most common getter material is titanium, which may be activated to provide a clean, active surface for reaction with the gas species. This can be effected by sublimation of the titanium by heating (for example resistance heating) to form a vapour of the titanium and the subsequent formation of the deposited “active” titanium surface by condensation of the titanium vapour.
Within ultra-high purity (UHP) gas processing applications, purifiers such as those previously described are often used to remove low levels of impurity, for example below 10's ppm, from the process environment. In certain vacuum processing applications, for example physical vapour deposition (PVD), these purifiers are also used to remove low partial pressures, for example below 10−2 mbar, of contaminate species. However, the problem with this approach is that the purifier has a finite capacity and while the units are sized to give an acceptable lifetime under normal operation, during fault conditions they may rapidly reach this limit and cease operation. Such purifiers also have a relatively low capacity to size ratio, so that a large getter/purifier is required to achieve a high capacity, or long life.
Furthermore, there are certain UHP gas and vacuum processing applications which generate exhaust streams comprising of an inert buffer gas with low levels of active contaminates. Examples include Xe in EUV (extreme ultra violet) applications, Ar in PVD applications and N2/Ar in ALCVD (atomic layer chemical vapour deposition) applications. In these applications the gas is often vented to the house scrubber or a POU (point of use) exhaust system.
The invention relates to a purifier that can provide a high capacity in a compact assembly, can tolerate fault conditions and has application in a wide range of gas processing applications.